Oscar Pistorious has been found guilty of culpable homicide and contravening the Firearms Control Act.
Judge Thokozile Masipa acquitted Oscar Pistorius of two of three weapons charges but found him guilty of the third.
Pistorius did not intend to kill Steenkamp, Masipa said, accepting his defence that he thought someone had broken into his house and that he believed he was defending himself.
Having recapped that Pistorius is not guilty of murder or premeditated murder, she said that Pistorius acted negligently when he fired shots through the door, knowing there was someone behind it.
The Olympic sprinter is accused of killing his girlfriend, Reeva Steenkamp.
Pistorius has not denied that he shot her, but claims it was an accident.
Culpable homicide is the South African term for unintentionally — but illegally — killing a person.
There is no mandatory minimum for negligent or culpable homicide. The maximum sentence is 15 years.
Pistorius has no prior convictions and it is expected that this would be taken into account during the sentencing phase.